Saturday, September 17, 2016

Legato Link

Legato Link is Pioneer's trademarked oversampling. In constrast to most oversampling with brick wall filtering, Legato Link deliberately seeks to capture high frequency information above the Nyquist Frequency (?). Some say it's merely a relatively slow rather than sharp brick wall digital filter--which might roll off highs earlier (but no evidence of that) or let some aliases through, and that appears to be possibly true, distortion levels would appear inconsequential to specification readers (the PD-75 for example specifies 0.0018, which would be -95dB, very respectible, out of -98.08 perfection).

Pioneer was doing interesting work in digital filtering from the beginning. And so were others. Pioneer used the term Legato Linear to refer to the highly refined filters in the PD-95 and comparable transport and recorder. In my mere PD-75, they used no such term, however as it was the A version and the PD-95 got the B version one suspects it was already developed along a similar direction. What Legato Linear means is not well explained, though we can guess the Linear has to do with things like linear phase response and/or linear filtering. There's little evidence that Pioneer was attempting to reconstruct high frequencies, as claimed for Legato Link, though the distortion seems to be slightly higher than absolutely necessary, 0.0018% is, so one expects a compromise is being made with that and pulse accuracy, and if that's the case then only 0.0018% is doing very well, say compared with those now who would go to 1% and beyond with NOS.

The actual usage of the term Legato Link and the hype about reconstructing high frequencies only occurrs much later, possibly with the CXD-500, and then becomes commonplace (with additional adjectives, like Super) in the Pioneer Elite DVD players (and, sadly perhaps, one reason I never bought one, I didn't trust them, as I should have).

However, it appears by some measurements, that actual performance fell a bit short of those inconsequential looking specs, still somewhat insequential looking:

Peter Aczel, for example measure -92dB above 800Hz, but down to -78dB in one channel, or 0.012%, around 250 Hz and below. He got identical performance in two units. Published in The Audio Critic.

Julian Hirsch got 0.004%, or -88dB, 20-20kHz, which he seemed to think was quite good.

(These of course inconsequential compared with NOS designs, which may get 10% distortion in some audible frequency ranges.)

One interesting question here, is this digital distortion, which might be much worse as it would increase proportionately at lower amplitudes?

Perhaps the use of Spline interpolation prevents the digital distortion from increasing so much at low frequencies. Anyway, now I'm a bit curious, and not at all turned off as I was by a friend in 1991 who showed me the pioneer advertisement:

I looked at that and said, that looks like aliasing distortion they're including. They can't include high frequency information. (Maybe they make it up by reasonable interpolation?) So it must be aliasing and grundge. I was highly skeptical, and moreso after reading various comments, reviews, and such regarding Pioneer machines. I mean, I wasn't into buying machines like that much anyway, I was satisfied with the performance of my Sony 507ES I purchased in 1989 and still works today (thanks to a bit of ingenuity on my part, partly). Anyway, Legato Link seemed like some sort of dangerous nonsense.

Meanwhile, in a somewhat pricier machine, also using bitstream dacs, Sony was getting -96dB 20-20k, and -97dB midband. (That was for the X997ES, one of the best measuring machines ever, since then it's been downhill mostly for CD performance. Perfection, again is -98.08dB and 0.001247% for THD+N.)

So color me as believing distortion perfection was being sacrificed in some way for time perfection. Ok, I'm much more interested now than I was in 1991. Very interested indeed, a lot of things from HDCD to SACD to HiRezPcm to MQA are all (or partly) about improving time accuracy, such as transient response.

For that reason and others I have some interest in the sound of the PD-75 with Legato Link and Pioneer Bitstream DAC's (which, btw have essentially perfect linearity down to anything you want, and have shown in some comparative measurements to have been, generally speaking models of comparative perfection) even if I've been (and will continue to be) doubtful of the full fidelity of anything 1-bit.

I really got the PD-75 as a transport, because the big mechanism, Me Tarzan or something, now it appears the clock is all important, wimpy transport with good clock is fine.

Still may be a decent transport, esp., with upgraded clock. But perhaps just use Onkyo RDV-1 already having fairly decent clock, and (for sonics) 1704's. And tis transport for anything allowing digital output. So this may be my goto-transport for now, actually for the best sound, until and if I keep (probably) and modify the Pioneer (I may just play the Pioneer as transport, as it works, for it's "vintage" sound, jitter and all, probably still at low levels, maybe even unmeasurable contribution to jitter from the transport itself, just enjoy the vintage feel, and sometimes even the perhaps slightly amplitude distorted sound--but with better time response.)

I have an Oppo BDP-95 available through about 100 ft of high end coax wire (my home wiring network plus interconnects). I'm not sure how much the spdif degrades, but I get perfect connectivity through my old Tact at 96/24. (88kHz on the Tact died even with short cables long ago, but 96kHz works fine)